A British dad and his wife fear their newborn baby may have been swapped by hospital staff and sold to traffickers after DNA tests revealed a child they were given was not theirs.

Richard Cushworth and his devastated Salvadoran wife Mercedes Casanellas have launched a desperate appeal to find their son after fearing he was swiped in hospital who thought his light skin would catch a high price on the black market.

The couple, who live in the United States, travelled to El Salvador so Ms Casanellas could give birth in her home country.

But after giving birth, the pair decided to have a DNA test while back in the US after noticing the child did not look like either of them - and discovered to their horror that the child wasn't theirs.

In an emotional interview with a local TV station, a teary Ms Casanellas said: "We haven't been able to sleep thinking about where he is, and who has him.

Appeal: Mercedes Casanellas, pictured with the wrong baby, is calling for people to come forward with information (Image: Collect)

"We just want them to give us our son back."

The parents fear their light-skinned baby was snatched deliberately by staff at the exclusive Ginecologico private hospital in the country's capital San Salvador to sell to child traffickers.

The family have reportedly already investigated all the other babies born at the hospital on the same day and found that all are with their correct parents - reinforcing their belief that their own son was stolen.

Mr Cushworth, who met Ms Casanellas when he worked as a missionary in El Salvador, said: "It's a horrible situation. I have a child and I don't know where he is.

"Someone took my child and I have no idea where he is, who is taking care of him, what has happened to him. Is he in the country? It's awful.

"I sometimes try not to think about this because it is so frightening."

Ms Casanella's obstretrician-gyneocologist, Dr Alejandra Guidos, who the couple accuse of masterminding the plot, was arrested on Thursday, according to their family's lawyer Francisco Meneses.

Ms Casanellas said that, from the fifth month of her pregnancy, she remembered how Dr Guidos would repeatedly tell her that her child would be dark-skinned, even though the father is white.

She said: "I always thought that was strange. How would he know that from the ultra-sound scans, and why would he keep saying it?"

Remembering her baby's birth, she said: "I was very stressed at first because the baby took a while to start breathing, but then I held him and remember thinking that he looked like my husband.

"He was very white and had similar features. I remember seeing his genitals and thinking that they were white and pinkish.

"But then the anesthetist came and told me that I was very nervous and that they were going to give me something to put me to sleep. After that I don't remember anything, until I woke up the next morning.

Dark: The parents noticed the child looked nothing like either of them (Image: Collect)

"Around 8am, they started to bring the babies to their mothers, and I waited for mine. But when I took him I saw that he was very different to the one I had held in the delivery room. When I changed his clothes I noticed that his genitals were very dark and not rosy like how I'd remembered.

"I said to the nurse, 'look, his genitals are very dark', and she told me, 'no, that's normal, that's normal'".

Ms Casanellas said photos she took of her baby son soon after the birth prove that the baby was white-skinned.

Despite the doubts, the couple took the baby back home to Dallas,, Texas, but over the coming months family and friends also noticed the child's darker colour and lack of resemblance with his parents.

Ms Casanellas said: "I would take photos of him and put them next to my husband, trying to find something of us in him. I kept trying to convince myself that he was really ours, that over time we would begin to see a resemblance.

"But my motherly instincts kept telling me that he wasn't mine."

The baby was three months old when the couple finally found to courage to take a DNA test, which showed he has a 0.00 per cent probability of being their son.

Desperate to find the baby she gave birth to, the couple rushed back to El Salvador.

Investigation: The parents were stunned when DNA tests showed neither of them was related to the child (Image: Collect)

At first San Salvador's Ginecologio hospital, considered the best private hospital in the country, denied that the baby could have been swapped, saying it was "impossible" due to their "high standards" of control.

But after Dr Guidos's arrest, following the family's high-profile TV interview, the hospital ordered an internal investigation and promised that the situation will be "rectified".

The country's Attorney General has now ordered a criminal investigation into the baby's disappearance amid claims a trafficking gang, led by Dr Guido, has been operating inside the hospital.

Ms Casanellas said: "I just want him to give me my baby back. I want to know that my child hasn't been trafficked or any other crime committed against him. I need my baby, I'm just asking for my baby."

The couple added that, if the true parents of the baby they were given are not found, they will raise him as their own.

She said: "If they can't find his mother, he already has parents, us. We are taking care of him and, even though we know he isn't our biological son, we still love him."